org.jctools.queues

Class SpscArrayQueue<E>

java.lang.Object

java.util.AbstractCollection<E>

java.util.AbstractQueue<E>

org.jctools.queues.ConcurrentCircularArrayQueue<E>

org.jctools.queues.SpscArrayQueue<E>

Type Parameters:

E -

All Implemented Interfaces:

Iterable<E>, Collection<E>, Queue<E>, IndexedQueueSizeUtil.IndexedQueue, MessagePassingQueue<E>, QueueProgressIndicators

public class SpscArrayQueue<E>
extends ConcurrentCircularArrayQueue<E>

A Single-Producer-Single-Consumer queue backed by a pre-allocated buffer.

This implementation is a mashup of the Fast Flow algorithm with an optimization of the offer method taken from the BQueue algorithm (a variation on Fast Flow), and adjusted to comply with Queue.offer semantics with regards to capacity.
For convenience the relevant papers are available in the resources folder:
2010 - Pisa - SPSC Queues on Shared Cache Multi-Core Systems.pdf
2012 - Junchang- BQueue- Efficient and Practical Queuing.pdf
This implementation is wait free.

Author:

nitsanw

Nested Class Summary

Nested classes/interfaces inherited from interface org.jctools.queues.MessagePassingQueue

MessagePassingQueue.Consumer<T>, MessagePassingQueue.ExitCondition, MessagePassingQueue.Supplier<T>, MessagePassingQueue.WaitStrategy

Field Summary

Fields

Modifier and Type	Field and Description
protected static long	C_INDEX_OFFSET
protected long	consumerIndex
protected int	lookAheadStep
static int	MAX_LOOK_AHEAD_STEP
protected static long	P_INDEX_OFFSET
protected long	producerIndex
protected long	producerLimit

Fields inherited from class org.jctools.queues.ConcurrentCircularArrayQueue

buffer, mask

Fields inherited from interface org.jctools.queues.MessagePassingQueue

UNBOUNDED_CAPACITY

Constructor Summary

Constructors

Constructor and Description
SpscArrayQueue(int capacity)

Method Summary

Modifier and Type	Method and Description
int	drain(MessagePassingQueue.Consumer<E> c) Remove all available item from the queue and hand to consume.
int	drain(MessagePassingQueue.Consumer<E> c, int limit) Remove up to limit elements from the queue and hand to consume.
void	drain(MessagePassingQueue.Consumer<E> c, MessagePassingQueue.WaitStrategy w, MessagePassingQueue.ExitCondition exit) Remove elements from the queue and hand to consume forever.
int	fill(MessagePassingQueue.Supplier<E> s) Stuff the queue with elements from the supplier.
int	fill(MessagePassingQueue.Supplier<E> s, int limit) Stuff the queue with up to limit elements from the supplier.
void	fill(MessagePassingQueue.Supplier<E> s, MessagePassingQueue.WaitStrategy w, MessagePassingQueue.ExitCondition e) Stuff the queue with elements from the supplier forever.
long	lvConsumerIndex()
long	lvProducerIndex()
boolean	offer(E e) Called from a producer thread subject to the restrictions appropriate to the implementation and according to the Queue.offer(Object) interface.
E	peek() Called from the consumer thread subject to the restrictions appropriate to the implementation and according to the Queue.peek() interface.
E	poll() Called from the consumer thread subject to the restrictions appropriate to the implementation and according to the Queue.poll() interface.
boolean	relaxedOffer(E message) Called from a producer thread subject to the restrictions appropriate to the implementation.
E	relaxedPeek() Called from the consumer thread subject to the restrictions appropriate to the implementation.
E	relaxedPoll() Called from the consumer thread subject to the restrictions appropriate to the implementation.
protected void	soConsumerIndex(long newValue)
protected void	soProducerIndex(long newValue)

Methods inherited from class org.jctools.queues.ConcurrentCircularArrayQueue

calcElementOffset, calcElementOffset, capacity, clear, currentConsumerIndex, currentProducerIndex, isEmpty, iterator, size, toString

Methods inherited from class java.util.AbstractQueue

add, addAll, element, remove

Methods inherited from class java.util.AbstractCollection

contains, containsAll, remove, removeAll, retainAll, toArray, toArray

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Collection

contains, containsAll, equals, hashCode, parallelStream, remove, removeAll, removeIf, retainAll, spliterator, stream, toArray, toArray

Methods inherited from interface java.lang.Iterable

forEach

Field Detail

consumerIndex

protected long consumerIndex

C_INDEX_OFFSET

protected static final long C_INDEX_OFFSET

P_INDEX_OFFSET

protected static final long P_INDEX_OFFSET

producerIndex

protected long producerIndex

producerLimit

protected long producerLimit

MAX_LOOK_AHEAD_STEP

public static final int MAX_LOOK_AHEAD_STEP

lookAheadStep

protected final int lookAheadStep

Constructor Detail

SpscArrayQueue

public SpscArrayQueue(int capacity)

Method Detail

offer

public boolean offer(E e)

Called from a producer thread subject to the restrictions appropriate to the implementation and according to the Queue.offer(Object) interface.

This implementation is correct for single producer thread use only.

Parameters:

e - not null, will throw NPE if it is

Returns:

true if element was inserted into the queue, false iff full

poll

public E poll()

Called from the consumer thread subject to the restrictions appropriate to the implementation and according to the Queue.poll() interface.

This implementation is correct for single consumer thread use only.

Returns:

a message from the queue if one is available, null iff empty

peek

public E peek()

Called from the consumer thread subject to the restrictions appropriate to the implementation and according to the Queue.peek() interface.

This implementation is correct for single consumer thread use only.

Returns:

a message from the queue if one is available, null iff empty

relaxedOffer

public boolean relaxedOffer(E message)

Description copied from interface: MessagePassingQueue

Called from a producer thread subject to the restrictions appropriate to the implementation. As opposed to Queue.offer(Object) this method may return false without the queue being full.

Parameters:

message - not null, will throw NPE if it is

Returns:

true if element was inserted into the queue, false if unable to offer

relaxedPoll

public E relaxedPoll()

Description copied from interface: MessagePassingQueue

Called from the consumer thread subject to the restrictions appropriate to the implementation. As opposed to Queue.poll() this method may return null without the queue being empty.

Returns:

a message from the queue if one is available, null if unable to poll

relaxedPeek

public E relaxedPeek()

Description copied from interface: MessagePassingQueue

Called from the consumer thread subject to the restrictions appropriate to the implementation. As opposed to Queue.peek() this method may return null without the queue being empty.

Returns:

a message from the queue if one is available, null if unable to peek

drain

public int drain(MessagePassingQueue.Consumer<E> c)

Description copied from interface: MessagePassingQueue

Remove all available item from the queue and hand to consume. This should be semantically similar to:
M m;
while((m = relaxedPoll()) != null){
c.accept(m);
}
There's no strong commitment to the queue being empty at the end of a drain. Called from a consumer thread subject to the restrictions appropriate to the implementation.

Returns:

the number of polled elements

fill

public int fill(MessagePassingQueue.Supplier<E> s)

Description copied from interface: MessagePassingQueue

Stuff the queue with elements from the supplier. Semantically similar to:
while(relaxedOffer(s.get());
There's no strong commitment to the queue being full at the end of a fill. Called from a producer thread subject to the restrictions appropriate to the implementation.

Returns:

the number of offered elements

drain

public int drain(MessagePassingQueue.Consumer<E> c,
                 int limit)

Description copied from interface: MessagePassingQueue

Remove up to limit elements from the queue and hand to consume. This should be semantically similar to:

 
   M m;
   int i = 0;
   for(;i < limit && (m = relaxedPoll()) != null; i++){
     c.accept(m);
   }
   return i;
 
 

There's no strong commitment to the queue being empty at the end of a drain. Called from a consumer thread subject to the restrictions appropriate to the implementation.

Returns:

the number of polled elements

fill

public int fill(MessagePassingQueue.Supplier<E> s,
                int limit)

Description copied from interface: MessagePassingQueue

Stuff the queue with up to limit elements from the supplier. Semantically similar to:

 
   for(int i=0; i < limit && relaxedOffer(s.get()); i++);

 
 

There's no strong commitment to the queue being full at the end of a fill. Called from a producer thread subject to the restrictions appropriate to the implementation.

Returns:

the number of offered elements

drain

public void drain(MessagePassingQueue.Consumer<E> c,
                  MessagePassingQueue.WaitStrategy w,
                  MessagePassingQueue.ExitCondition exit)

Description copied from interface: MessagePassingQueue

Remove elements from the queue and hand to consume forever. Semantically similar to:

 
  int idleCounter = 0;
  while (exit.keepRunning()) {
      E e = relaxedPoll();
      if(e==null){
          idleCounter = wait.idle(idleCounter);
          continue;
      }
      idleCounter = 0;
      c.accept(e);
  }
 
 

Called from a consumer thread subject to the restrictions appropriate to the implementation.

fill

public void fill(MessagePassingQueue.Supplier<E> s,
                 MessagePassingQueue.WaitStrategy w,
                 MessagePassingQueue.ExitCondition e)

Description copied from interface: MessagePassingQueue

Stuff the queue with elements from the supplier forever. Semantically similar to:

 
  int idleCounter = 0;
  while (exit.keepRunning()) {
      E e = s.get();
      while (!relaxedOffer(e)) {
          idleCounter = wait.idle(idleCounter);
          continue;
      }
      idleCounter = 0;
  }
 
 

Called from a producer thread subject to the restrictions appropriate to the implementation.

lvConsumerIndex

public final long lvConsumerIndex()

soConsumerIndex

protected final void soConsumerIndex(long newValue)

lvProducerIndex

public final long lvProducerIndex()

soProducerIndex

protected final void soProducerIndex(long newValue)